The present invention relates to an apparatus for forming a thin film suitable for use in production of semiconductor devices such as ICs and LSIs.
Conventionally, various apparatus and methods have been known such as CVD and PVD methods and apparatus. In general, CVD method provides a high reactivity, while PVD enables formation of a fine strong thin film in a highly evacuated atmosphere.
One type of apparatus for forming a thin film is known which has a source of evaporation, a counter electrode holding a substrate on which a thin film is to be formed by vapor deposition such that the substrate opposes the source, a grid disposed between the source and the counter electrode, and a filament disposed between the grid and the source for generating thermions, wherein the grid is held at a positive potential with respect to the filament during the operation. This type of apparatus is disclosed, for example, in Japanese patent application Laying Open No. 59-89763.
In this type of apparatus, the substance evaporated from the source is ionized by the thermions emitted from the filament. The ionized substance is then accelerated upon passing through the grid by an electric field which is directed towards the electrode, so that the ionized substance is collided with and deposited on the substrate whereby a film with a high degree of adhesion to the substrate is formed on the substrate.
The above mentioned type of apparatus, however, suffers from the following disadvantages. Namely, when a thin insulating film is formed on the substrate, the grid also is coated with an insulating film, with the result that dielectric breakdown between the grid and the filament or between the grid and the counter electrode happens so that the desired reacting condition in the vacuum container can no more be maintained, with the result that formation of a uniform thin film is failed. The same problem is encountered also when a thin conductive film is formed subsequently to the formation of a thin insulating film in the same apparatus. Namely, during the formation of the thin conductive film, the dielectric breakdown happens to fail the formation of a uniform thin film.
In addition, the known apparatus for forming a thin film has encountered the problems of the adhesion between the substrate and the thin film formed thereon being insufficient and of difficulty in forming a film on a substrate which is made of a material having a relatively small heat-resistance, e.g., plastics.
Furthermore, in the known apparatus for forming a thin film, characteristics of the thin film formed on a substrate tend to change when the configuration and/or the size of the vacuum container are changed, even when factors such as shapes of the source of evaporation, filament, grid and the counter electrode and, spacings and electrical conditions of these components are unchanged.